It just goes to show that with replacements you can never be sure that you have all the dates!
Several people did a lot of research on these in the 1980s and 1990s—looking through bundles of notes—to track all the prefixes, and to record the replacements as they were being issued, and for long after they had been in circulation.
Still recording to be done though.

Last week, a previously unrecorded date turned up for CCC on £10 notes:
25.10.81